Scotland in April is a gamble; if the weather is good there’s nothing like it, though when it’s bad, well, the same is true, in a very different way. A gamble for a car launch then, even more so when the ride in question is a drop-top. Oh, and one with 666bhp, too. I’ve an advantage, though; I know these roads, many being formative in my early driving years. North of Glasgow on the west coast, Scotland has some spectacular driving blacktop, world-beating scenery and local traffic that doesn’t mind being overtaken. Good thing, too, as the McLaren 675LT Spider is monstrously quick. Not that we’ll be V-maxing it today, as the local police might not take too kindly to a 326kph run here. Nor will it be necessary; having driven the 675LT coupé recently at the Silverstone F1 circuit there’s no question about the veracity of the numbers McLaren associates with its limited-run LT cars.

This is the third McLaren to wear the LT moniker and it, like its fixed-roof relation, will only be built in a series of 500 cars. If you’ve not already got your order in then you’re too late, as it’s sold out. The coupé was over-subscribed, so the Spider came about due to customer demand. The 675LT takes its name from its illustrious McLaren F1 relation, specifically the limited-series Long Tail (shortened to LT) cars that were required to homologate it for continued success in international racing. The 675LT coupé pulled off the name a bit more convincingly; the Spider, arguably, less so in concept. However, speaking to the people behind it reveals that, while it inevitably features a kerb weight higher than its sibling, it too has been rigorously engineered to the LT formula. To recap, that means the 650S Spider it’s based upon has undergone significant re-engineering, with the sort of fastidious attention to detail that McLaren is famous for.

Weighing 1,270kg, it’s 100kg lighter than the 650S Spider, though some 40kg more than the 675LT coupé. To achieve that, McLaren used even more expensive weave in its bodywork, as well as inside — the carbon bucket seats borrowed from the P1 save a combined 15kg, for example. There’s thinner glass as well (1.0mm or so on the windscreen), saving a further 3kg. The titanium exhaust saves 1.1kg, while its crossover design helps reduce back pressure, and the changes to the 650S’s 3.8-litre twin-turbo V8 engine are so extensive it gains a unique engine code, M838TL.

Some 50 per cent of the engine’s components have been redesigned to increase performance and efficiency, and reduce weight. The two turbochargers are unique to the LT, the compressors machined from solid material rather than cast, allowing maximum airflow to the combustion chambers, with the benefit of less heat added to it. The turbochargers’ wastegates feature electronic rather than pneumatic recirculation to improve retardation when lifting off, benefitting throttle response, while lighter con rods and camshafts also help improve the engine’s immediacy and performance.

All that, combined with the weight loss, allows the 675LT Spider to reach 100kph in 2.9 seconds, 200kph in 8.1 seconds and 300kph in 23.6 seconds; numbers that would see even the iconic McLaren F1 recede into the 675LT Spider’s mirrors, until the old-timer pulls out its 372kph top-speed party trick — at which point it would pass the LT.

The knack with speed today is keeping it down, as the 675LT Spider’s natural gait is evidently greater than the limits around here. Abstaining from the seemingly endless push from that 3.8-litre V89 is revealing, though, as the Spider’s talents are far deeper than the mere pursuit of ultimate velocity. That Scottish launch location turns out to be a masterstroke, as the need to keep the 675LT reined in allows more opportunity to better understand the fundamentals of its make up. Crucially, that centres around the way it drives. McLaren’s signature from its first series production car, the 12C, with which the 675LT Spider shares its DNA, is the unusual combination of taut, fine control, mated to a ride quality that’s more luxury saloon than supercar. Or near hypercar in relation to the 675LT Spider; the loss of the roof evidently creates virtually no difference in how it rides and handles. Mark Gayton, project manager at McLaren Cars, admits that his team did tweak the suspension slightly over the coupé’s to account for the 40kg difference in kerb weight, though it was a product of his team’s obsessive attention to detail rather than real necessity.

The 675LT Spider’s suspension is derived from the P1’s, its geometry unique, with a 20mm wider track and lighter components throughout to reduce unsprung mass. Spring rates are up 27 per cent at the front and 63 per cent at the rear, helping accommodate the 40 per cent increase in downforce the aerodynamic revisions bring over its 650S Spider relation. The wheel and tyre package includes a 19in front rim and a 20in rear, with specially developed Pirelli P Zero Trofeo R tyres. The wheels are held on by titanium wheel bolts, instead of the standard steel ones used on the 650S Spider. That suspension is adjustable too, and famously does without anti-roll bars; the 675LT Spider features McLaren’s ProActive Chassis Control (PCC), which uses hydraulically linked dampers with a gas-filled accumulator, allowing the precise roll control, yet it can decouple for a compliant ride and excellent wheel articulation.

Without the distraction of speed, the 675LT’s finest qualities are immediately apparent. The steering is incisive, its crispness allied to a weighting that’s perfect. Mark Vinnels, executive director, Product Development, says that a lot of that is down to the retention of a hydraulic system, and McLaren is yet to test an electrically assisted power steering set-up that’s able to deliver the level of feel and precision the company demands. That’s quite an admission, though it absolutely underlines the firm’s commitment to developing engaging drivers’ cars. The LT models, and to a lesser extent the 650S before it, exemplify McLaren’s push to offer cars with more of the intangible elements in their driving make up, such as feel and emotion. Turn that wheel and the reward isn’t just the immediacy of response, but the fine weighting and the texture through its rim. The 675LT Spider delivers the sort of snappy detail that’s now largely absent from all but the most hardcore of driving machines. That precision and feel is in no way to be confused with harshness, as the steering is not so busy as to be intrusive; it delivers the perfect level of information about the road surface and topography. In other supercars and sportscars you’d find yourself bracing or wincing in anticipation of heavy knocks from the suspension, ultimately to the detriment of pace, but the 675LT Spider’s ride allows it to maintain its speed with little fuss, even on weather-ravaged Scottish roads.

In Scotland, it’s obvious McLaren has achieved its goal of increasing driver appeal, the inherently stiff MonoCell meaning, unlike its supercar rivals, that there’s no perceivable sacrifice in control or agility depending on your preference as to an open or closed car — the 675LT Spider feeling every bit as torsionally rigid as its coupé relation, only with the enhanced ability of dropping the top when the mood and weather allows. In April, those opportunities are scant around here, though the sun does make a brief appearance for the run along the coast road following Loch Fyne, on the way back to Loch Lomond, offering a chance to drop the folding hard-top above, and better hear the 3.8-litre V8 twin-turbo in all its glory.

Like the breaks in the weather, the opportunities to really delight in running the engine behind up to its 8,500rpm indicated redline are few, though the occasional long, clear and, crucially, sighted stretches of road do allow the odd indulgence at higher engine speeds. Push the accelerator to the floor and the way the 675LT Spider gains momentum is genuinely startling, the engine’s keenness to rev is unlike most forced induction units, likewise its tone, which, thanks in part to that titanium exhaust and loss of sound deadening, is rich and exotic in its timbre, if not quite as visceral as its few remaining naturally aspirated rivals. The Spider has the same engineered-in or, more accurately, not engineered out, vibration and slight harshness, the smoothness of its 650S Spider relation replaced with a harder edge that’s more in keeping with the LT’s more obvious focus.

You’ll run out of road before gears if chasing that redline, and the paddle-shifted seven-speed transmission, like the chassis and electronic driver stability and traction aids, offers three differing settings. Track mode is too much for the road, Sport is quick enough, though in truth you’re unlikely to find the normal setting in any way lacking in its quickness to shift. The paddle-shifters retain the McLaren trick of being linked, like the Formula 1 cars, so a pull on one side sees it fall away on the other; it’s a delightful reminder of both McLaren’s F1 link and its determination to be different. Other areas here are less successful, such as the portrait layout of the sat-nav screen, which is all but impossible to see in sunlight — and the buttons around it need a bit of learning. Seemingly minor things, but they jar in what’s otherwise an incredibly well-rounded and ridiculously capable package.

An extraordinary car, whatever road you’re on, the 675LT Spider is all the better here for its apparently ill-advised launch location, demonstrating that there’s more to it than just raw speed, with real driver appeal at ordinary speeds on roads that would undoubtedly show up its rivals’ deficiencies.